Murine virus (FLV)-induced erythroleukemic cells can be induced to differentiate along the erythroid pathway when grown in the presence of DMSO or DMF. BUdR inhibits these stimulatory effects. Using this model system, we propose to continue our studies on the pathogenesis of leukemia and the basic mechanism involved in the suppression of this disease. Among the aspects to be studied are: (1) The mechanism of action of compounds which stimulate or inhibit differentiation, (2) whether or not these effects are always reversible, (3) whether or not the stimulatory effects are cell cycle-dependent, and (4) properties of the clones which are responsive and unresponsive to DMSO stimulation.